Hydrocarbon fuels having improved antiknock properties



conditions mentioned above.

HYDROCARBON FUELS HAVING I1VIPROVED ANTIKNOCK PROPERTIES Charles A. Sandy and James H. Werntz, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 18, 1957 Serial No. 640,575

Claims. (Cl. 123-1) This invention relates to fuels, and more particularly to fuels with improved knock resistance when used over the-entire operating range of internal combustion engines.

It is recognized that internal combustion engines knock under a wide variety of engine operating conditions, including varying speeds, degree of spark advance, compression ratio, fuel/ air mixture ratio, temperatures, and intake manifold pressure. Because of these variations in engine conditions, the engine may knock under mild or severe stress. Industry recognizes that mild stress is usually encountered when the engine knocks under conditions of relatively low speed, retarded spark or low operating temperatures such as is normally experienced in the operation of the existing type passenger car. Onthe other hand, severe stress is encountered under conditions of high engine speeds, advanced spark, high operating temperatures or high manifold pressures such as encountered with high speed operation of automotive type engines or the normal operation of aviation engines. I

The development of internal combustion engines of high compression ratios has established a need for high quality fuels having increased resistance to knock over the above mentioned wide range of engine operating conditions. Careful refining and blending of fuel components can produce a fuel of sufliciently increased knock resistance to satisfy the engine requirements under the previously mentioned conditions. Usually, however, tetraethyllead is today employed in these fuel blends to improve the knock resistance which cannot easily and economically be obtained through refining techniques. Tetraethyllead is widely used since it does impart improved antiknock quality over the wide range of engine The use of tetraethyllead, however, has limitations. Each successive increment of tetraethyllead produces only a fraction of the improvement in antiknock rating obtained with each previous increment. Certain fuels for spark ignition engines, particularly those containing large proportions of aromatic and/or olefinic components, respond rather poorly to tetraethyllead, especially at the normal upper limit of 3 ml. of tetraethyllead per gallon in automotive engihes,'or 4.6 ml. per gallon in aviation engines.

' hole in the head by means of an adapter, and is supplied It is an object of the present invention to provide 1 new and improved antiknock compounds which function over the entire range of engine operating conditions. It is a further object of this invention to provide new and improved antiknock compounds for fuels already containingtetraethyllead, which increase knock resistance to a degree not attainable by the use of tetraethyllead alone. Itis a still further objectof this invention to provide antiknock compounds which are superior to tetraethyl- 2,935,974 Patented May 10, 1960 ice . lead under severe operating conditions such as normally encountered in aircraft or in the newly proposed high compression automotive engines.

It has now been found that lithium salts of organic secondary carboxylic acids, in which the carboxy group is attached to a carbon atoni which has two of theremaining three valences attached to two different carbon atoms and the third valence is attached to hydrogen, are very efiective antiknock compounds for fuels when such fuels are used over the entire range of operating con- These acids therefore have the following gen ditions. eral formula CH-OOOH where R in each case stands for a hydrocarbon radical;

of a ring system. The acids to be used according to the present invention are preferably those containing from 4 to 18 carbon atoms including the carboxy group.

The compositions of the present invention are particularly applicable for use in engines equipped with fuel injection systems, since with ordinary carburetion' manyof these additives are not sufficiently inductable to avoid deposition in the intake system over an extended period of operation. These compounds, however, are eifective irrespective of the method by which they are introduced into the cylinder of the car. While they are normally introduced with the fuel itself, they may be introduced separately as a dust or powder, or with solvents used either to carry them alone or in the supplementary antiknock solutions such as the water/alcohol mixtures employed in aircraft engines or tetraethyllead/ alcohol mixtures employed in automotive engines.

,To illustrate this invention, a number of examples are given in which comparisons show the effectiveness of the compounds of the present invention in clear and leaded fuels.

In Examples 1 to VH, inclusive, fuel samples were-- tested under both mild and severe test conditions in a Waukesha ASTM D909-49T knocktest method single. cylinder knock rating engine equipped with a four-hole position for this type engine, a rate of change of pres sure pick-up and a steel plug occupy three of the four A Waukesha ASTM D909-49'T holes in the head. knock test method fuel injector is inserted into the fourth is determined at the trace knock intensity level by means of the rate of change of pressure pick-up mounted in the cylinder head. The signal from the pick-up feeds intoa cathode-ray oscilloscope and the occurrence of knock is'fobserved as a shattering of the rate of change of pressure trace on the oscilloscope screen late in the engine cycle.

Under these operating conditions, the knock resistance of all fuels tested in this specification is determined by comparing the highest useable knock-free compression ratio of these fuels to that of primary reference fuels consisting of blends of isooctane and normal-heptane below 100 performance number, and isooctane plus tetra.- ethyllead above 100 performance number. The knock resistance of all fuels tested is expressed in this specification in terms of Army-Navy Performance Numbers as defined in Tables VII and VIII in the ASTM aviation method ('D-6l449T), as recorded in the ASTM Manual of Engine Test Methods for Rating Fuels, published. by the American Society for Testing Materials, October 1952.

These tests and the test conditions were developed to evaluate antiknock compounds under the same stresses as would be encountered in automotive operation.

The, gasoline used in the Examples I through VI is a typical commercial type gasoline having a clearF-l Research rating of 87 octane numbers.

Example I To a sample of a gasoline containing 3.0 ml. of tetraethyllead per gallon and 190 ml. of methanol per gallon as a solubilizing assistant and having a performance number of 100 in the mild test and 85 in the severe test, 4.5 grams of lithium Z-ethylbutyrate per gallon was added. Asa result the performance numbers were raised to 107 in the mild test and to 96 in the severe test.

Example II Example III To .a sample of gasoline containing 3.0 ml. of tetraethyllead per gallon and 190 ml. of methanol per gallon as a solubilizing assistant and having a performance number of 102 in the mild test and 81 in the severe test, 8.84 grams of lithium 2,3-dicyclohexylpropionate per gal- Inn was added. As a result the performance numbers were raised to 108 in the mild test and to 89in the severe test.

Example IV To a sample of a gasoline containing 3.0 ml. of tetraethyllead per gallon and 190 ml. of methanol per gallon as a solubilizing assistant and having a performance number of 103 in the mild test and 78 in the severe test, 4.85 grams of lithium cyclohexane carboxylate per gallon was added. As a result the performance numbers were raised to 108 in the mild test and to 83 in the severe test.

Example V To a sample of a gasoline containing 3.0 ml. of tetraethyllead per gallon and 190 ml. of methanol per gallon as a solubilizing assistant and having a performance number of 108 in the mild test and 80 in the severe test, 7.89 grams of lithium diphenylacetate per pallon was added. As a result, the performance numbers were raised to 113 in the mild test and to 84 in the severe test.

Example VI To a sample of a gasoline containing 3.0 ml. of tetraethyllead per gallon and 152 ml. of Cellosolve per gallon as a solubilizing assistant and having a performance number of 98 in the mild test and 81 in the severe test, 6.8 grams of lithium 2-methyl-2-neopentylcyclopropane carboxylate per gallon was added. As a result, the performance numbers were raised to 107 in the mild test and 91 in the severe test.

Example VII To a sample of a gasoline containing 190 ml. of methanol per gallon as a solubilizing assistant and having a performance number of 80 in the mild test and 69 in the severe test, 5.42 grams of lithium 2-ethylhexanoate per gallon was added. As a result, the performance numbers were raised to 87 in the mild test and to 74 in the severe test.

In Examples VIII to X inclusive the tests were carriedout in an engine equipped with manifold fuel injection in accordance with the ASTM procedure indicated to show the knock resistance of fuels by the supercharge method.

Example VIII To each of two samples of commercial aviation gasoline containing 4.07 ml. of tetraethyllead per gallon and 190 ml. of ethanol per gallon as a solubilizing assistant and having a performance number of by the ASTM' D909-49T knock test method, lithium 2-ethylhexanoate was added in quantities so that the blended gasoline contained 1.36 grams .per gallon and 2.71 respectively. As a result, the performance numbers were raised to and 161 respectively in the ASTM D-909-49T knock test method.

Example IX To a sample of isooctane containing 1.5 ml. of tetraethyllead per gallon was added an ethanol solution of lithium Z-ethylbutyrate so that the finished blend contained 76 ml. of ethanol per gallon and 1.32 grams per gallon of the lithium compound. As a result, the performance number of leaded isooctane was raised from 133 to above 161 in the ASTM D-90949T knock test method.

Example X To each of two samplesv of isooctane was added an ethanol. solution of lithium Z-ethylbutyrate so that the finished blend contained 76 ml. of ethanol per gallon and 0.44 grams per gallon and 1.32 grams per gallon of the lithium compound respectively. As a result, the pen formance number of isooctane was raised from 100 to 138 and 158 respectively in the ASTM D-909-49T knock test method. Even at concentrations of 0.05 gram of the lithium compound per gallon, a significant improvemnt in performance number is obtained.

The amount aid the solution of the lithium compounds does not materially affect the performance number of the fuel.

In general, the lithium compounds of secondary carboxylic acids employed in this invention may be prepared by reacting, the appropriate acidic organic compound with lithium or lithium hydride, hydroxide, alkoxide or carbonate. The carboxylates are readily obtained on neutralizing the free, acid with any lithium base,.

grams per gallonof solvent used in the above examples to.

Alternatively, they may be prepared by saponification of an ester with a lithium base. It is convenient to prepare the compounds in aqueous systems, subsequently removing water by drum drying, spray drying or other conventional processes.

This invention is applicable to hydrocarbon fuels forinternal combustion engines and more 'particularlyto fuels which may be a mixture of hydrocarbons boiling in the gasoline range, or arefined gasoline as defined in the ASTM designation D-288-53 (adopted 1939, revised 1953). The invention is especially useful in fuels of 40 performance number or higher isu'ch as.;those' used in spark ignition engines of either automotive or aviation type over their entire range of operation. However, the compounds of this invention are antiknocks in lower quality fuels of the kerosene or JP-4 types (jet turbine fuel) which are employed in heavy duty spark ignition engines such as tractors, etc. e 3

The lithium salts employed in the present invention are effective in clear fuels and those fuels containing tetraethyllead in an amount up to 6.0 ml. of tetraethyllead per gallon. These fuels may be finished fuels which may contain varying amounts of conventional fuel additives such as scavenging agents, dyes, antioxidants, antiicing agents; inhibitors for rust, corrosion, haze formation, gum formation; anti-preignition agents, etc.

The hydrocarbon fuels in which the additives of the present invention may be incorporated may or may, not contain blending agents to enhance the solubility of the lithium compounds of this specification in the fuel. Typical blending agents are those set forth in the examples, although other blending agents such as gasoline miscible alcohols, glycols, esters, ketones, amides, and other polar organic liquids may be used. The lithium salts may be dissolved directly in the blended gasoline or added as a concentrated solution in a blending agent.

The amount of lithium compound normally employed will of course vary with the quality and the intended end use of the fuel. Normally the amount of lithium compound employed will vary from 0.05 gram to 50 grams per gallon of fuel, the preferred range being between 0.5 to grams per gallon regardless of the amount of tetraethyllead employed in the fuel. In contrast to the behavior of tetraethyllead, additional increments of these lithium compounds usually produce improvements in knock-resistance approximating that obtained with the previous increment; that is, a graph of the response of fuels to these additives will be substantially linear.

The lithium salts of secondary carboxylic acids of from 4 to 18 carbon atoms improve the performance numbers of gasoline-type fuels when employed in the amounts specified above. In addition to those employed in the specific examples above given, the lithium salts of other acids may be substituted in the above examples to give enhanced knock resistance such as: lithium Z-methylproionate, lithium Z-methylbutanoate, lithium Z-cyclopenfrlpropionate, lithium 2-methyl-3-cyclohexylpropionate, lithium 2-ethyl-3,4-dimethylhexanoate, lithium Z-methylcylohexane carboxylate and lithium 3,4,8,9-tetramethylundecane-S carboxylate.

In addition to the marked antiknock elfect of the lithium salts of secondary carboxylic acids, it has been found that the maximum knock-free power, as measured in the ASTM D-909-49T knock test method, occurred at a significantly leaner fuel/air ratio than that of the untreated fuels when these lithium compounds were employed to raise the performance number near or above the rating limit of the engine, which is 161 performance number.

A still further advantage of the use of the lithium salts of the present invention, particularly in aircraft engine operation, is the fact that they not only show marked antiknock effects under rich fuel/ air ratio conditions, as

measuredbythe-AS'DM D-'909-49T knock'tes't method, but'also show marked antiknock activity at lean fuel/air ratios employed in normal cruising flight of aircraft.

What is claimed is: I 1. A hydrocarbon fuel for spark ignition internal combustion engines, containing from about 0.05 gram to about 50 grams per gallon of a lithium salt of a secondary carboxylic acid of the formula per gallon of a lithium salt of a secondary carboxylic acid of the formula v err-coon in which R'in, each case stands for a hydrocarbon radical,

including where they jointly stand for a cycloaliphatic ring, said carboxylic'acidcontaining from 4 to 18 carbon atoms.

3. A hydrocarbon fuel for spark ignition internal cornbustion engines, containing from 0.5 gram to 20 grams per gallon of the lithium salt of 2-ethylhexanoic acid.

4. A hydrocarbon fuel for spark ignition internal combustion engines, containing from 0.5 gram to 20 grams per gallon of the lithium salt of '2-ethylbutanoic acid.

5. In the method of operating a spark ignition internal combustion engine in which the fuel is introduced into the combustion chambers of the cylinders under subatmospheric to superatmospheric pressures, the step which comprises improving the knock resistance of the fuel by introducing into the combustion chamber so that it is present at the time the fuel is ignited, a lithium salt of a secondary carboxylic acid at the rate of from 0.05 gram to 50 grams per gallon of fuel, said carboxylic acid having the formula CH-CO0H in which R in each case stands for a hydrocarbon radical, including where they jointly stand for a cycloaliphatic ring, said carboxylic acid containing from 4 to 18 carbon atoms.

6. In the method of operating a spark ignition internal combustion engine in which the fuel is introduced into in which R in each case stands for a hydrocarbon radical, including where they jointly stand for a cycloaliphatic ring, said carboxylic acid containing from 4 to 18 carbon atoms.

7. A hydrocarbon fuel for spark ignition internal combustion engines containing up to 6.0 m1. of tetraethyl lead err-coon in which R in each case stands for a hydrocarbon radical, including where they jointly stand for a cycloaliphatic ring, said carboxylic acid containing from 4 to 18 carbon atoms.

8. A hydrocarbon fuel for spark ignition internal combustion engines containing up to 6.0 ml. of tetraethyl lead and'from 0.5 gram to 20 grams per gallon of a lithium salt of a secondary carboxylic acid of the formula CH-COOH in which R in each case stands for a hydrocarbon-radical; including where they jointly stand for a cycloaliphatic ring, said carboxylic acid containing from 4 to 18 carbon atoms.

9. A hydrocarbon fuel for spark ignition combustion engines containing from about 0.05 gram to about 50 grams per gallon of a lithium salt of an open chains'econdary carboxylic acid containing from 4 to 18 carbon atoms in which the organic radical 'attached' to the carboxyl group is a hydrocarbon radical.

mm the; method of operating-a spark ignition internal combustion engine inwhich the fuel is introducedinto. the combustion chambers of the cylinders under superatmospheric to subatmospheric pressures, the step "which comprises improving the knock resistance of the fuel by introducing into the combustion chamber, so

that it is present at the time the fuel is ignited, a lithium salt of an open-chain secondary carboxylic acid containing. from 4 to 18 carbon atoms in which the organic radical attached to the carboxyl group is a hydrocarbon radical, at the rate of from 0.05 gram to 50 grams per gallon of fuel.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Journal of Institution of Petroleum Technologists, February-December- 1927', vol. 13, pp. 244-255, The Effect ofMetallic Vapors on the Ignition of Substances, by

Egerton and Gates. 

5. IN THE METHOD OF OPERATING A SPARK IGNITION INTERNAL COMBUSTION ENGINE IN WHICH THE FUEL IS INTRODUCED INTO THE COMBUSTION CHAMBERS OF THE CYLINDERS UNDER SUBATMOSPHERIC TO SUPERATMOSPHERIC PRESSURES, THE STEP WHICH COMPRISES IMPROVING THE KNOCK RESISTANCE OF THE FUEL BY INTRODUCING INTO THE COMBUSTION CHAMBER SO THAT IT IS PRESENT AT THE TIME THE FUEL IS IGNITED, A LITHIUM SALT OF A SECONDARY CARBOXYLIC ACID AT THE RATE OF FROM 0.05 GRAM TO 50 GRAMS PER GALLON OF FUEL, SAID CARBOXYLIC ACID HAVING THE FORMULA 